Goat Cheese Souffles in Phyllo Cups with Frisée Salad

PreparationMake cups: Preheat oven to 375°F. Cover stack of phyllo with 2 overlapping sheets of plastic wrap and a dampened kitchen towel. Put 1 phyllo sheet on a work surface and brush with some butter, then top with 2 more sheets of phyllo, brushing each with butter. Cut buttered stack into 6 (4 1/2-inch) squares with a sharp knife, trimming sides as needed. Line each of 6 muffin cups with a square. Make 6 more phyllo cups (4 are extra, in case of breakage) in same manner with remaining pastry sheets and butter. Bake cups in middle of oven until golden, about 8 minutes, then cool completely in pan on a rack. Make filling: Increase oven temperature to 400°F. While cups are cooling, melt butter in a 3-quart heavy saucepan over moderately low heat, then whisk in flour. Cook roux, whisking, 3 minutes. Add milk in a stream, whisking, and bringto a boil, whisking. Reduce heat and simmer, whisking occasionally, 5 minutes. Remove from heat and whisk in mustard, yolks, and 1/4 cup Parmigiano-Reggiano until combined, then fold in goat cheese. (Cover surface of mixture with wax paper if not using immediately.) Beat egg whites in a large bowl with an electric mixer until they just hold stiff peaks. Fold one third of whites into sauce to lighten, then fold in remaining whites gently but thoroughly. Spoon batter into 8 phyllo cups and sprinkle with remaining Parmigiano-Reggiano. Bake in middle of oven until soufflés are puffed and golden, about 15 minutes. Make salad while soufflés bake: Whisk together vinegar, mustard, and salt in a bowl, then add oil in a slow stream, whisking until emulsified. Just before soufflés are ready, toss frisée and radishes in a large bowl with just enough dressing to coat. Mound salad onto 8 plates and sprinkle with chives, then make a small nest in center of each. Place a soufflé cup in each salad and serve immediately. Cooks' notes:• Phyllo cups can be made 1 day ahead and kept in pan, carefully wrapped in plastic wrap, at room temperature. (Extra phyllo cups can be filled with ice cream or fruit for dessert the next day.) • Soufflé filling (without egg whites) can be made 1 day ahead and chilled, covered. Bring to room temperature and stir (to loosen) before proceeding.